Black-tailed Godwits and Volcanic Eruptions

Around 360 earthquakes were detected in Iceland in the week beginning 4 December, which is pretty normal. Earthquakes can give hints about impending volcanic eruptions so they’re important to Icelanders –  and, by implication, to Icelandic waders too.


In the long term, volcanic ash provides the nutrients that improve fertility, as you can read in How volcanic eruptions help waders, but short-term effects can be seriously negative. This was what Tómas Gunnarsson discovered when he went out to count godwit broods at what should have been the height of the 2011 breeding season. He found only two pairs that showed signs of having broods. Was the Grímsvötn eruption between 21 and 28 May to blame?

Assessing producivity

Iceland hosts internationally important breeding populations of several wader species, including almost the entire population of the islandica subspecies of Black-tailed Godwits. For several years, wader biologists in Iceland have been monitoring the breeding performance of Black-tailed Godwits in the Southern Lowlands, by counting pairs with broods along a 198 km transect. Their theory was that breeding performance would be better in warm years because of the advantages of early nesting in warm springs.

graphWith six years of data, a team drawn from the universities of Iceland, Aveiro (Portugal) and East Anglia (UK) have published a paper in the BOU Journal IBIS, which fouses upon the relationship between spring temperature and the number of Black-tailed Godwit broods. In the top graph, taken from the paper, it is clear that there is a lot of variation in productivity, with the lower graph showing a strong association between mean May temperatures and the number of Black-tailed Godwit pairs with chicks. What stands out is  the outlier for 2011, which is excluded from the calculations that produce the regression line. For the five other years R² = 0.94, indicating a very close link between May temperature and productivity, as predicted. Using the mean temperature for May 2011, the number of pairs of godwits with chicks that might have been expected to have been seen in 2011 is about 25 – rather than just two.

The full methods can be viewed in this paper:

Effects of spring temperature and volcanic eruptions on wder productivity. Tómas Grétar Gunnarsson, Lilja Jóhannesdóttir, José A Alves, Böðvar Þórisson & Jennifer A Gill. IBIS (2017) DOI: 10.1111/ibi.12449

The ash effect


Eyjafjallajokull in 2010

We all remember the eruption of Eyjafjallajökull in 2010. This produced copious amounts of ash, most of which was blown south to mainland Europe, disrupting air travel. Grimsvötn, which erupted in May 2011, was less famous but actually depositied a lot more ash in Iceland, especially in the Southern Lowlands.


Ash  covered pools and clogged insect traps

On dry days, fieldworkers working in this study area used face masks to protect their respiration, as simply walking through vegetation disturbed large amounts of ash into the air. A layer of ash was frequently observed covering pools in wetlands and traps for invertebrate sampling were often clogged with ash. Short-term negative effects of volcanic dust on birds have been reported previously, probably acting through increased invertebrate mortality, and the low count of successful broods in the warm summer of 2011 seems to bear this out.


An alarming parent godwit

By monitoring breeding Black-tailed Godwits in southern Iceland, the wader scientists have shown that volcanic activity can have a major impact  on bird productivity. Productivity was back to what appears to be normal (when corrected for mean temperature) by the next summer. The lack of recruitment in 2011 seems to have been reflected in a slight decrease in the counts of Black-tailed Godwits in the United Kingdom in the winter 2011/12 (as measured by WeBS counts), with a resumption in what is generally an upward population trend in 2012/13.

The rapid recovery of productivity in the year following the volcanic eruption (2012) indicates that the negative effects of the incident seem to be have been short in duration. Whimbrels in the same region were also affected by volcanic activity in the summer of the 2011 eruption (Katrínardóttir et al. 2015). In the long-term, the effects of volcanic activity on waders in Iceland are most likely to be positive, as volcanic dust recharges vegetated land with nutrients and buffers pH. Densities of waders across Iceland are generally higher where volcanic dust inputs are higher (Gunnarsson et al. 2015).

singleThis study shows how annual variation in productivity can vary greatly in response to rare and extreme events. As expected for a long-lived species, effects of a single year of very low productivity were short in duration and probably had a limited effect on the population growth rate. The pronounced effect that spring temperature has on annual variation in productivity is likely to be a more significant factor in the future population trajectory of waders, given the ongoing and rapid warming of Arctic and Sub-arctic regions.

Effects of spring temperature and volcanic eruptions on wder productivity. Tómas Grétar Gunnarsson, Lilja Jóhannesdóttir, José A Alves, Böðvar Þórisson & Jennifer A Gill. IBIS (2017) DOI: 10.1111/ibi.12449

GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.


Overtaking on Migration

When two legs are better than one: the spring migration of Black-tailed Godwits.

headerThe winter range of Icelandic Black-tailed Godwits covers a relatively wide latitudinal spread, from southern Spain to Scotland.  Even though not at the extremes of this distribution, a flock of birds in Lisbon experiences very different mid-winter conditions to a flock of birds in Liverpool.  December days never get shorter than 9hr 27min in Lisbon, which is 2 hours more than in Liverpool, and the average maximum daytime temperature is 14⁰C, as opposed to 6⁰C.  On the negative side, it’s a lot further from Iceland to Portugal than it is to northern England.


José Alves enjoying warm winter conditions in Portugal

In other studies (of Avocets and Cormorants, for instance) it has been shown that individual birds that winter close to their breeding areas are able to arrive back earlier in the spring than ones that winter further away.  This is not the case in Black-tailed Godwits and this paper, published in Oikos in 2012, explains why.

Overtaking on migration: does longer distance migration always incur a penalty? José A. Alves , Tómas G. Gunnarsson , Peter M. Potts , Guillaume Gélinaud , William J. Sutherland and Jennifer A. Gill


A team from the universities of East Anglia (UK), Iceland and Aveiro (Portugal) has been monitoring the spring arrival dates of colour-ringed Icelandic Black-tailed Godwits since 2000. The most recent paper to use this data-set has shown that adult birds have remarkably fixed arrival times in Iceland (to within a few days), and that the advancing arrival of the godwit population has been driven by young birds travelling to Iceland for the first time (see  By tracking individual birds and the countries from which they travel, it is clear that the earliest arrivals are actually birds that winter in the southern part of the range – not the birds from northern and central parts of Great Britain, which have about 1500 km less far to travel.


Black-tailed Godwits on the Tagus estuary (Lisbon)

For birds migrating south from arctic and subarctic breeding grounds, a trade-off might be expected between distance and conditions experienced during winter months. Birds travelling further south are likely to experience much more benign conditions, while those that undertake shorter flights expend less energy and may have the potential to return home earlier or to pick up clues as to the likely conditions they will face on breeding grounds in the early spring.

Work by Tómas Gunnarsson has shown links between arrival of Black-tailed Godwits in Iceland and subsequent breeding success. In areas where most territories are occupied early in the season, over half of pairs fledge youngsters whilst in areas where most territories are occupied later in the spring fewer than half of pairs are successful.  You can read more here.

The easy life in Portugal


Portuguese rice fields provide alternative feeding opportunities for Black-tailed Godwits

José Alves studied Icelandic Black-tailed Godwits wintering in Portugal as part of his PhD at the University of East Anglia. One of the papers from this work, focusing on energetics and migration strategies, was published in Ecology in 2013:

Costs, benefits, and fitness consequences of different migratory strategies. José A. Alves , Tómas G. Gunnarsson , Daniel B. Hayhow, Graham F. Appleton, Peter M. Potts , Guillaume Gélinaud , William J. Sutherland and Jennifer A. Gill

energy-figThe paper shows that energetic conditions for wintering godwits are better in Portugal than further north in the winter range

  • Warmer air temperatures and considerably lower wind speeds mean that thermoregulatory costs, and hence energetic requirements, are lower for godwits wintering in west Portugal than in south Ireland or east England.
  • Black-tailed Godwits wintering in Portugal have access to larger numbers of bigger bivalves for the whole winter period. Birds wintering in eastern England or Ireland rarely find these big packages of protein.
  • On average, foraging for c.5 hours per day provides sufficient intake for a Portuguese-wintering Black-tailed Godwit.
  • In Ireland, the food supplies available on mudflats during the daylight hours of a tidal cycle are not sufficient, and godwits also forage on nearby grasslands.
  • In eastern England, rapid depletion of food supplies on estuaries means that resources become very limited in late winter, and are often not sufficient to meet the energy requirements of wintering godwits.

Clearly, Portugal is a great place to spend the winter. It’s just a long way from Iceland.

The Spring Overtake


The direct route from Portugal to Iceland may be possible but most go via The Netherlands

Portuguese Black-tailed Godwits travel further to their winter site but they break their spring migration into two legs, with most birds moving to the Netherlands in February or March and others staging in France, Great Britain and Ireland. By using Colin Pennycuick’s model ‘Flight’ (Pennycuick, C. J. 2008. Modelling the flying bird. – Academic Press), José Alves and his colleagues investigated the range of spring migration strategies available to individuals, given their body masses. Of Portuguese-wintering Black-tailed Godwits, around 10% are predicted to be able to reach the breeding grounds in one flight. From sightings of colour-ringed birds, it is clear that the vast majority of Portuguese birds do not make direct flights. It is possible that some individuals fly straight to Iceland but no bird has yet been proven to take this option.

When a small number of Black-tailed Godwits were caught in Portugal, just prior to the normal departure time, the masses of individuals were remarkably good predictors of their subsequent movements.

  • The lightest male was predicted to be unable to reach even the first possible stop-over site, in France, and indeed this bird remained in Portugal throughout the breeding season.
  • Of two males with just sufficient mass to reach France, one did indeed get to France and the other remained in Portugal during that breeding season (but did migrate the following year).
  • The remaining seven males were predicted to be able to reach the major stop-over sites in the Netherlands or in east England (both of which are about 1750 km from west Portugal). Thanks to the wonderful network of observers, every one of these birds was spotted in these staging areas. These birds included RO-YGf (below)dutch-bird
  • The only two females caught were both later recorded in the Netherlands; the heavier one was seen shortly after ringing and the lighter one arrived later, possibly having spent time in France.

Black-tailed Godwits are well watched and often deliver day-by-day records. For this species, colour-rings are a cheap and simple technology with which to study migration. You can read more about the network of colour-ring readers in the WaderTales blog, Godwits & Godwiteers.

The Oikos paper goes on to discuss the strategies being employed by Black-tailed Godwits, relating these to the importance of getting to Iceland early. You can read more here:

Overtaking on migration: does longer distance migration always incur a penalty? José A. Alves , Tómas G. Gunnarsson , Peter M. Potts , Guillaume Gélinaud , William J. Sutherland and Jennifer A. Gill

In Conclusion

Portuguese Black-tailed Godwits make full advantage of benign winter conditions in Portugal and then fly north very early in spring. By moving to the Netherlands (or Britain & Ireland) they are taking up pole position for the race to Iceland.

GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.


A place to roost

Safe roost sites are important for waders such as Black-tailed Godwits

top-picIt has been said that Black-tailed Godwits are the laziest birds in the world, usually in a frustrated tone while waiting for a marked bird to wake up and reveal the rest of its colour rings. Roosting is not laziness, however; it’s an important resource conservation strategy in the daily balance of energy inputs and outputs.

When Black-tailed Godwits are feeding in tidal systems they have a limited amount of time each day to access the shellfish and worms that make up their diet. These foods are unavailable over the high-tide period, and sometimes in the lull between the ebb and flood, so birds conserve energy by gathering together at roosts. They seek out sites which are safe and sheltered and go to sleep – often for several hours if undisturbed. Theunis Piersma and colleagues have shown that sleep is the most energy efficient form of activity for shorebirds.

In two interesting papers, focusing on Red Knot and Great Knot in Roebuck Bay, North-Western Australia, Danny Rogers and colleagues showed that choice of roost sites seems to involve several criteria:

  • Birds try to find a roost as close as possible to feeding sites, probably to reduce travel costs between feeding areas and high-tide roosts.
  • In particular, birds appear to turn down feeding opportunities that take them further from preferred roost sites.
  • Open roosting sites that provide clear views of any approaching predators seem to be preferred
  • Availability of safe night-time roosts seems to be more restricted, with birds flying further to find a suitable site to wait out the high tide period.
  • The estimated ‘commuting costs’ associated with flying to and from these roosts accounted for between 2% and 8% of daily energy expenditure.
  • Flocks of Knot that were disturbed at roosts and forced to fly around for thirty minutes had an estimated increase in their daily energy expenditure of c 13%.
  • roosting-curlew

    These Curlew, roosting on the shores of the Humber, are minimising energy expenditure in very cold conditions

    Temperatures in Roebuck Bay can frequently exceed 38⁰C, and the waders chose wet sites in which they could keep their feet and legs cool. That’s not a problem for waders wintering in the UK.

The details can be found here:

What does this mean for Black-tailed Godwit in UK conditions?


Waders often roost in mixed flocks. These birds are resting on an Icelandic beach after crossing the Atlantic

Although the facts, figures and conclusions listed above relate to Red Knot and Great Knot, the authors point out that they gather in mixed roosts with other species to which similar decision-making might apply. The Australian studies took place in very hot conditions but many of the factors influencing roosting site choice are likely to also apply to our cold and wind-swept estuaries in NW Europe. For instance, a study of Knot on the Dee Estuary by Mitchell et al in England estimated that costs of commuting to roosts could account for 14% of daily energy expenditure.

energy-figEnergetic constraints are likely to present different issues for arctic waders that spend the non-breeding season in the northern hemisphere than for ones that choose to cross the equator, and experience warmer conditions and heat stress. Even within Europe, the energetic balances that waders can experience on different estuaries can vary widely. In their 2013 Ecology paper on Black-tailed Godwit energetics, Costs, benefits, and fitness consequences of different migratory strategies  José Alves and colleagues showed that mild weather and abundant food supplies result in a positive energy balance for godwits wintering on the Tagus estuary in Portugal and, to a lesser extent, the estuaries of south Ireland. In east England estuaries, however, the costs of keeping warm can sometimes exceed the energy available from the food supplies (see figure). In such circumstances, an undisturbed roost, located as close as possible to feeding areas may well be especially important.

Consequences of roost loss


Colour-marked Redshank demonstrated the individual consequences of habitat loss

Although it is very hard to demonstrate population-level consequences of removing roosting sites, we have some clues about the how birds respond to removal of roosts and foraging sites from impact assessment work carried out by the BTO on Redshank in the Cardiff Bay area. When this bay was closed and flooded for commercial development, Redshanks lost both feeding areas and traditional roosting sites. Tracking of colour-ringed Redshanks showed that displaced birds moved to new feeding areas and roost sites up to 19 km away, but mostly stayed close-by on the mudflats of the River Rhymney. Cannon-net catches of these flocks provided measurements of bird mass before and after the closure of the Bay, which revealed that adult Redshank from the Bay had difficulty in maintaining body condition in the first winter following closure and that their survival rates in subsequent winters remained lower than birds that had previously been settled in the Rhymney area. Three papers are essential reading for anyone interested in the consequences of displacements caused by development projects.

ynrx-for-blogA key point of both the Knot work in Australia and the Redshank impact assessment study in Wales is the energetic costs to individuals that can result from the disruption caused by the loss of roosting or foraging sites. Indeed, individual waders may even have favoured locations within roosts that they consistently use. For example, at Gilroy Nature Park, a shallow pool where up to 3500 of the Black-tailed Godwits that feed on the Dee estuary in NW England regularly gather to roost, observers of colour-ringed birds have noticed that marked individual godwits (eg YN-RX pictured here) are often seen in exactly the same place within the pool and flock.  Losing a roosting site of which individuals have such detailed knowledge, and forcing flocks of birds to find alternative roosting locations, may therefore have bigger consequences than just the kilometres covered.

Importance of individual sites

mapThe total number of Icelandic Black-tailed godwits was estimated to be 47,000 in 2004, a figure that is likely to be closer to 60,000 now as the population has continued to grow. This means that a flock of 3,000 birds represents about 5% of the total of the entire breeding population. There is a small number of sites across the United Kingdom that hold these sorts of numbers at different stages of the year. According to the latest figures from the Wetland Bird Survey, numbers on the Wash and Humber estuaries in east England peak at averages of 8198 and 3413 in September, there are 4339 Black-tailed Godwits on the Welsh side of the Dee estuary in October and 5909 on the English side in November. The mean count on the Thames also peaks in November (5883). As the winter progresses, numbers on the nearby Ribble estuary rise to a mean of 4234 in January, there is a mean maximum of 3236 on the Washes in February and 3191 on the Blackwater in March. Although all of these sites are important to Icelandic Black-tailed Godwits throughout the non-breeding period, the different timing of peak counts illustrates the reliance of Icelandic birds on a network of sites. To get a feel for the range of strategies used by individual birds, see Godwits and Godwiteers.



Roosting Black-tailed  Godwits at Gilroy Nature Reserve share their pool with a horse and Canada Geese

While estuarine feeding areas across Europe are well safeguarded, through the network of Special Protection Areas, roost sites are not always as well served, especially if birds spend the high tide period on sites outside the SPA boundary of their foraging areas, such as the freshwater pool at Gilroy Nature Reserve, inland of the Dee Estuary. Some roost sites such as North Killingholme Haven Pits on the Humber have been included within a designated SPA formed by the adjacent mudflats but others, such as Gilroy, are discrete sites outside the SPA. Maintaining the wader populations that forage on our estuarine mudflats may depend upon our capacity to protect their safe roosting sites, even if they are not currently designated.

GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.


Establishing breeding requirements of Whimbrel

Breeding Whimbrel may be associated with wet heaths but chicks need small pools and ditches too


One of the advantages for waders (shorebirds) is that parents can lead their chicks to suitable feeding areas almost as soon as they are hatched. This means that the habitat in which parents choose to secrete their nests can be very different to the habitat in which their youngsters will later forage.

ad-for-blogAs part of a study into the potential impacts of a large wind farm proposal on Shetland, a team from Alba Ecology Ltd and Natural Research Projects Ltd collected data on the habitat associations of wader species, particularly Whimbrel, on Mainland Shetland. A new paper, in the BTO journal Bird Study shows that habitats used by Whimbrel chicks for feeding are significantly different to those used by adults for feeding and nesting.

Habitat characteristics of breeding Eurasian Whimbrel Numenius phaeopus on Mainland Shetland, Scotland, UK by Kate Massey, Peter Cosgrove, Fergus Massey, Digger Jackson & Mark Chapman

Fourteen sites across Mainland Shetland were studied, in order to identify the three main requirements of Whimbrel – adult territorial and foraging habitats, nest site habitats and chick feeding habitats. The sites were spread across central and west Mainland Shetland, focusing on areas regularly used by breeding Whimbrel. Between them, these held between 90 and 100 pairs, out of a local total of 150 local pairs.

chick-for-blogWhilst adult Whimbrels used blanket bog, dominated by ling heather, cottongrass and other species associated with wet heath, when both nesting and feeding, the structure of habitats used by chicks was very different. These were characterized by small, wet and often linear features, with plenty of mosses and plants such as purple moor-grass and bulbous rush. The presence of these flashes, ditches and former peat-cuttings may be crucial to the successful breeding of Whimbrels.

Sad times for the Curlew family

curlew IUCN

Based on IUCN BirdLife assessments

As outlined in the blog Is the Curlew really near-threatened? we have probably already lost 2 out of 8 of the members of the curlew family – definitely Eskimo Curlew and possibly Slender-billed Curlew. Although Whimbrels are not currently causing official concern, there is certainly a need to be watchful. This paper is therefore an important addition to the written information about the habitat requirements of the species. The conclusions reached by the authors may well be of interest to scientists tackling tricky issues relating to the conservation of European Curlew. Across Wales and Ireland, breeding populations have been decimated (literally).

 Providing the right habitat for Shetland’s Whimbrel

 For Shetland’s Whimbrel, the habitat differences between adult feeding/nesting locations and chick foraging locations were very striking and suggest that the presence of both types of habitat may be of importance. Chicks move out of the heavily grazed open heather areas, in which nests are often made, and into wetter and taller, mixed, and structurally-diverse vegetation, where it is easier to hide from predators such as gulls, corvids and skuas, and to find food. If suitable habitat for Whimbrel chick foraging is limited, then chick growth and survival may be compromised. This paper suggests that management aimed at benefiting breeding Whimbrel needs to address the habitat needs of chicks, in terms of wet features, as well as the habitat needs of adults for foraging and nesting. You can read more in the paper.


Grazed heather areas (left) are favoured by feeding and nesting adults, while chicks prefer wet flashes (right). Photos: Peter Cosgrove

 Work on other upland wader species has shown that food availability, vegetation structure and cover from predators may at least partly explain habitat preferences of chicks. When tracking Golden Plover families in northern England, Mark Whittingham and colleagues found that chicks selected the edges of marshy habitats. They recommended that drainage ditches should be blocked, in order to provide more suitable feeding habitat. An added benefit of this sort of measure is that more water is held on moorland, which helps to reduce flooding downstream.

Lowland wet grasslands in Broads

Shallow ditches increase Lapwing productivity: Mike Page/RSPB

As Peter Cosgrove, one of the authors of the new paper has commented, “The more I read and discover about wader chicks, the more I see the importance of small, wet flushes with cover – maybe this is a general feature of many species?” As you can read in A helping hand for Lapwings, the provision of wet features, particularly foot-drains, is crucial to the successful fledging of species in a more open landscape.

A matter of scale?

Creating the right habitat mosaic for adults and chicks will depend upon the scale of the movements of family parties of the wader species that is causing conservation concerns. Tómas Gunnarsson reports that family groups of Icelandic Black-tailed Godwits can cover large distances. One brood of small chicks (less than five days old) was found a week later 3 km away. Whimbrels may be able to select areas with suitable nesting and nearby chick-rearing potential or perhaps they can also move their chicks longer distances, if necessary? Research into the movements of family parties might tell us whether moving chicks for a kilometre or more could have adverse consequences, in terms of growth or survival. Presumably, adults would prefer to find the right mix of habitats within relatively close proximity, which suggests that managing grazed heath to provide a suitable mosaic of cover for nests, areas of short vegetation and wet features may be a sensible conservation prescription for Whimbrel.

Habitat characteristics of breeding Eurasian Whimbrel Numenius phaeopus on Mainland Shetland, Scotland, UK by Kate Massey, Peter Cosgrove, Fergus Massey, Digger Jackson & Mark Chapman

GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.





Snipe & Jack Snipe in the UK and Ireland

This blog first appeared as an article in Shooting Times and Country magazine. It has been amended to provide more web links.


A wisp of Common Snipe

There’s a big difference between the number of Common Snipe and Jack Snipe we see in the United Kingdom each winter, with an estimated 1,100,000 of the former and 110,000 of the latter, according to the authors of Population Estimates of Bird in Great Britain and the United Kingdom. They remind us that Jack Snipe are hard to find and identify and warn that the total of 110,000 is a contender for ‘least reliable’ of the hundreds that have been compiled for this mammoth stock-take.


Comparative measurements (summarised from work by Guy-Noel Olivier)

In theory, therefore, for every ten Common Snipe we see we ought to see one Jack Snipe. Telling them apart is mostly a matter of size (see table) and there’s a useful identification video that has been produced by the British Trust for Ornithology. Both species make good use of their striped, cryptic plumage to avoid detection but Jack Snipe take the art to the next level, hiding against or under a tussock until the last possible moment and then exploding from beneath a person’s feet. Given the closeness of approach, perhaps Jack Snipes might be more obvious and their numbers exaggerated?


Jack Snipe probing in mud

In the winter months, Jack Snipe are not as closely associated with wetlands as are Common Snipe, preferring longer vegetation, such as that to be found in muddy, cow-poached rough grazing marsh, to the open edges of larger bodies of water. For the tiny Jack Snipe, a cow’s hoof-print forms an ideal pool in which to probe. One of the areas that birdwatchers go to see Jack Snipe is Glasgow. Strange though it may seem, several of the wetland areas within the city limits hold small numbers of birds, especially in autumn, when migrating Jack Snipe pass through Britain, on their way from Scandinavia to wintering areas in south-west Europe. Members of the local ringing group have focused a lot of effort on this species, catching individuals by dragging a mist-net through the rough, wet, reedy grassland and ringing birds that have jumped from the ground as the net passed over them. See blog by Gillian Dinsmore.


Jack Snipe are relatively long-winged

Jack Snipe are well designed for migration, with much bigger wings for the size of the body than the Snipe. Unlike Common Snipe, many of which migrate in flocks, or wisps, Jack Snipe are thought to travel mostly alone and at night. They cover long distances, with some birds from Russia crossing the Sahara and those from eastern areas of Siberia travelling to eastern Africa, India and southern coastal countries of mainland Asia. The birds that winter in the British Isles have much less far to travel than the majority of the population, therefore.

Common Snipe, which are much bigger and more common than Jack Snipe, start to appear in their wintering areas as early as August. The pioneering birds are juveniles; most adults moulting at least some of their flight feathers before flying south and west in September and October. We know this because many French hunters have provided wings to scientists studying the age and sex structure of the population in that country. Moulting is an energetically expensive part of any bird’s life, so autumn feeding conditions are presumably generally good enough for moult to have been at least started, if not finished, before birds leave the breeding areas. Not every bird manages to fit in a full moult before it’s time to move south, however, with one in six adults shot in France found to be in suspended moult, having shed and moulted some primary feathers before migration, with a view to completion in the wintering grounds. A slightly smaller number have a mixed age of secondary flight feathers and about a quarter delay completion of covert moult.


Common Snipe

Although most of the Common Snipe we see in Britain in the wintertime have come from Scandinavia and mainland Europe, Ireland has a strong additional connection to Iceland. A quarter of foreign-ringed Common Snipe discovered in Ireland or Northern Ireland have been found to be wearing Icelandic rings, compared to 1 out of 255 in England, none in Wales and just 10% in Scotland. This and lots of other fascinating facts about migration come to light because hunters kindly send information about ringed birds to The British Trust for Ornithology, which is ‘mission control’ for ringing in both the UK and Ireland. This information is available on-line via the BTO website.

Across Europe, although there is almost certainly a decline in the number of Common Snipe, probably linked to man’s incessant drive to drain wetlands, there is no suggestion as yet that Common Snipe should be added to the list of species of conservation concern. For British and Irish breeding birds the situation is very different, however. By the time of the first national bird surveys, some 50 years ago, we had been turning wetlands into farmland for as much as 2000 years and, since then, numbers of Common Snipe may well have fallen by a further 90% in the areas in which they are still breeding. There has been a major shrinkage of the species’ range since 1968-72. Losses are shown as downward triangles in the map from the latest Bird Atlas, published by the British Trust for Ornithology. The rate of decline across England, Wales, southern Scotland and much of Ireland in the shorter period since 1988-91 emphasises just how quickly the species is being lost. It can only be a matter of time until Common Snipe is added to the red list of species of conservation concern in the UK, in order to highlight the perilous plight of our breeding population.



Displaying Common Snipe

A displaying Common Snipe is a magical thing – flying around with real purpose, climbing into the sky and vibrating its tail feathers in a stooping descent. Our grandparents could have heard them drumming on grazing marshes anywhere in the country and just imagine what the fens of eastern England must have been like 500 years ago. These days, most people in southern Britain will have to visit a nature reserve even to have a chance to share that same magic. I am lucky enough to go to Iceland every summer, where I can still easily see a dozen Common Snipe displaying at the same time above areas of wet grassland.  If you want anything like the same sort of experience in the UK, you’ll probably need to travel to the Outer Hebrides.

GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.



Bar-tailed Godwits: migration & survival

Putting the flags out –  to learn more about one of the most amazing species of migrating wader.

Ruth banner

When we caught 505 Bar-tailed Godwits on the Wash, on the east coast of England, on 29 August 1976 we thought that we would add hugely to our knowledge of the species’ migration but we were disappointed. In the last six years, by adding leg-flags to just 248 birds, the Wash Wader Ringing Group has learnt a lot more.

Forty years ago

On 29 August 1976, in the days of stubble-burning, we had covered four cannon nets with fine, black burnt chaff to hide them almost completely. We knew that the big tide would push birds off the saltings and over the sea wall, there were decoys to pull the birds into the right 1% of a vast, flat field and the weather was good. Everything was ready. I was in a one-man, cabbage-crate hide, in line with my set of two nets. I remember seeing one Redshank look at the decoys and descend, pulling down a vast cloud of over 2000 Bar-tailed Godwits. There were some concerns about birds being too close to one of the nets on my line so we fired three nets, catching 505 bar-tailed godwits and 44 other waders.

Cathy ad and juv

Juvenile with moulting adult

A catch of 505 Bar-tailed Godwits seemed like a game-changer, including 22 that were already wearing rings. 483 new birds were bound to make a huge difference to our understanding of the species’ migration patterns and survival probabilities … surely? Up until that day, the Wash Wader Ringing Group (WWRG) had ringed a total of 1136 Bar-tailed Godwits so we were adding over 40% to the total, using harder rings with a much longer life-expectancy than those added as early as 1959.

This was a moulting flock; an autumn drop in numbers and a previous recovery of a bird in Spain suggested that many birds would spend the winter elsewhere but where? As luck would have it, only one of the birds from August 1976 has ever been found abroad – a bird shot in France in February 1985. The only British recoveries have been a bird found dead in Yorkshire in November 1976 and seven birds found around the Wash between 1979 and 1999. As to subsequent recaptures, 38 birds have been caught again by the WWRG, five of which were retrapped for a third time. With all the best models in the world, these figures are not enough to give a reasonable estimate of survival and there is no way that a change in survival rate could be picked up.

It’s pleasing to report that one bird was still alive on 21 February 2003 – over 28 years after ringing – but even this is not the longevity record for a BTO Bar-tailed Godwit. That’s held by another WWRG bird that was ringed on 22 August 1974 and last recaptured on 4 August 2008 – nearly 34 years later. Perhaps one of the 1976 birds is still alive and waiting to be caught again?

Bar-tailed Godwit migration

Since the 1976 catch, WWRG has been a bit more fortunate in its foreign recoveries of metal-ringed Bar-tailed Godwit, with 2 recoveries in Mauritania, one in Guinea Bissau and another on a ship off Guinea, out of a total of 12 BTO-ringed birds found in Africa. A bird caught in Teesmouth on 13 October 1982 was in Western Sahara five days later, which may give an indication of the timing of post-moult movement. The map alongside shows the full set of BTO recoveries (purple) and foreign-ringed birds found in Britain & Ireland (orange). The dots show the westward post-breeding movement from Russia to the Atlantic coast of Europe and the onward migration of thousands of birds to Africa.

One of the fascinating things about migration is the way that different populations of the same species have developed radically different migration patterns since the last Ice Age, the global maximum extent of which was reached only 20,000 years ago. At the same time that the Bar-tailed Godwits we see in Western Europe are making relatively modest journeys west and south in late summer, some of those of the baueri subspecies are undertaking nine-day, non-stop flights from Alaska to New Zealand. The physiological processes and navigational techniques that birds on the Pacific flyway have mastered would amaze their European cousins. To read more about flyway evolution for Arctic waders, and Knot on particular, see a Review by Theunis Piersema (Journal of Ornithology, 2011).

Conservation Status

Bar-tailed Godwits are classified as near-threatened by BirdLife International and the IUCN. There are four recognised subspecies facing various threats, as shown in the species fact-sheet here. 

Sam winter gloves

Bar-tailed Godwits wintering on the Wash are of the lapponica subspecies

Two subspecies visit the Wash Special Protection Area (SPA); lapponica from Norway through to western Siberia and taymyrensis from central Siberia. Two subspecies, menzbieri and baueri, use the East Asian-Australasian Flyway and are both undergoing extremely rapid declines, in large part due to severe habitat loss in the Yellow Sea. As a result of severe problems for waders using this flyway, the species has been uplisted to Near Threatened (BIrdLife International).

Satellite-tagging has revealed the impressive trans-oceanic migration routes of individuals between Alaska and New Zealand and shown the importance of the Yellow Sea for birds as they return north in the spring. Colour-rings and flags have shown that there has been a sudden drop in survival rates for Bar-tailed Godwits and other species using sites in China and other rapidly developing countries of South-East Asia, leading to urgent calls for conservation initiatives at an international scale. You can read more about this emerging story in these three papers.


Learn more about the amazing migration of Bar-tailed Godwits on the New Zealand Science Learning Hub

Contrasting extreme long-distance migration patterns in bar-tailed godwit Limosa lapponica. Phil Battley et al. Journal of Avian Biology. 10.1111/j.1600-048X.2011.05473.x 

Simultaneous declines in summer survival of three shorebird species signals a flyway at risk. Theunis Piersma at al. Journal of Animal Ecology. 10.1111/1365-2664.12582

Declining adult survival of New Zealand Bar-tailed Godwits during 2005–2012 despite apparent population stability. Jesse Conklin et al. Emu.

For Bar-tailed Godwits wintering in western Europe there is currently less immediate conservation concern, although there are warming conditions in their breeding grounds and over-fishing and emerging diseases of shellfish are known to be affecting estuaries on both sides of the North Sea. Things are more worrying in West Africa, where numbers have declined from 746,000 to 498,000 over a period of 30 years, according to a report by van Roomen et al. Some of these birds spend time in the Wash in the autumn on their way south.

Status of coastal waterbird populations in the East Atlantic Flyway. With special attention to flyway populations making use of the Wadden Sea. van Roomen et al.

Flying the flag

Cathy gluing

Each bird wears a two-letter flag and a white colour-ring (shown here)

Given the worsening conservation status of Bar-tailed Godwits and the gaps in our understanding of what is happening to birds that visit the Wash SPA, the WWRG decided that it would help if birds could be monitored through colour-ringing. That way, the movement and survival of individuals can be monitored using a telescope instead of relying on recapture.

The flagging of Bar-tailed Godwits on the Wash has dramatically increased the number of records of birds subsequent to ringing but the scheme is still in its early days. Flagging started in August 2010 but the first significant catch did not take place until 11 February 2012, when 56 birds was flagged. According to Phil Atkinson, who runs the WWRG database for the species, one third of the birds from this catch have been resighted alive in the four years since that catch (compared to 1% recapture rate for metal-ringed birds in the four years after the 1976 catch).

Cathy KAMost resightings have been on the Wash and those from elsewhere have tended to confirm what was known from metal ringing. A moulting bird on the Wash was seen on the Wirral (northwest England) in the same autumn, showing that birds moulting on the Wash can move elsewhere in Northwest Europe to winter. A non-moulting bird, caught at Terrington on 30 September 2011, was resighted at Ebel Khaznaya, Mauritania 50 days later. These two resightings confirmed that the Wash is an important site not only for the wintering Fenno-Scandinavian and western Siberian lapponica breeding populations but also central Siberian taymyrensis birds, that pass through in autumn to wintering areas in West Africa. The majority of overseas records have come from the Wadden Sea in spring and autumn, when birds have been on return passage to the breeding areas. There’s a 1996 summary of migratory movements of metal-ringed WWRG birds here:

The origins, moult, movements and changes in numbers of Bar-tailed Godwits Limosa lapponica on the Wash, England, Bird Study. 

Aivar Estonia

UV was spotted in Estonia in August 2012

By the end of 2015, 248 Bar-tailed Godwits had been colour-ringed and 92 of them seen again, many locally on the Wash. These high resighting rates are a consequence of focused searches by WWRG members and reports from birdwatchers submitting their records to Over the next few years it will be possible to estimate annual survival probabilities and to monitor how these change in the medium to long term. As was shown in the Yellow Sea, spotting a dramatic drop in colour-ring return rates provides evidence that development pressures are having an impact upon migratory species. Worsening conditions in the breeding grounds or wintering areas could well be detected through a more gradual but no less serious reduction in survival rates.

GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.


Lapwing moult

In most northern waders, post-breeding moult is a distinct phase – between autumn migration and the start of winter – but it’s different for Lapwings

Lapwing header

Primary moult is one of the key stages of a wader’s life. Knowing the length of the period in which birds are constrained by this energetic process may be really important to our understanding of the whole annual cycle of waders. In Oystercatchers, for instance, it has been shown that they cannot finish their primary moult in periods of low food abundance. One or more of the outer pairs of primaries are retained, becoming more faded and worn as the next twelve months pass and providing a signal of a previous period of stress. [See BTO report 238 by Atkinson et al.]

Lapwing in flight

The shape of a Lapwing’s wing is very different to that of most wader’s in the UK

Lapwing moult was first studied in detail in the 1970s using an innovative technique that did not require birds to be captured. By collecting primary feathers dropped by a flock of Lapwings that spent several weeks near their Buckinghamshire home, David and Barbara Snow were able to estimate the duration of moult. They did not start picking up feathers until August in 1974 but they were ready for the start of the 1975 season and captured a whole season’s worth of data that year, visiting the site every four days during a long, dry summer.

Primary wing moult

For flocks of waders in Britain and Ireland, autumn moult is generally squeezed in between their return from the arctic and sub-arctic breeding grounds and the start of winter, when days get shorter, the weather gets colder and much of the prey becomes less numerous and harder to access. In the late summer, adult birds start to discard the colourful feathers that they grew in spring and the main wing and tail feathers that have served them well for the best part of a year. The key period of moult is the time in which the ten primary feathers are replaced. The inner one (primary 1) on each wing is dropped first and the outer one is last. Each of the ten primary feathers is scored from 0 to 5, so an old wing has a score of 0 and a new wing has a score of 50. During the process, there is a gap in the wing, where new feathers are growing. A typical bird in mid-moult might have ten feathers scored as 5554332100 (moult score 28), with primary four nearly fully grown and primary eight newly discarded. Unsurprisingly, flight capacity is impeded. It’s not a great time to migrate – unless you happen to be a Lapwing.

David & Barbara Snow


The primary feathers of a Lapwing are unusually distinctive

David & Barbara Snow were each respected ornithologists in their own right and David was the author of the BTO’s Guide to Moult in Birds and senior scientist in the bird section of what is now the Natural History Museum. Wherever they lived or worked – from Trinidad to Tring – they observed the birds around them, so when a flock of Lapwings gathered to moult near their home they decided to collect the feathers that they dropped. They discovered that it is possible to use the individual patterns of white spots and the lengths of primary feathers in order to assign primary number to discarded Lapwing feathers, and that this could be done with certainty for primaries 1, 2, 7 and 10 (with 1 being the innermost). Reference to a small sample of BTO moult cards allowed David & Barbara to assign moult scores of 1, 4, 29 and 41 to the points at which these four distinct feathers had been dropped and collected. The synchrony of moult in the two wings was evident: “Several times we found pairs of feathers lying exactly where they had been dropped, separated by a body width”.

Much of what the Snows discovered from recording in detail the feathers shed by their local flock of 70 and 120 moulting Lapwing in 1974 and 1975 is still relevant. They suggest that the collection of dropped feathers might be a useful adjunct to the study of moult in situations where birds roost in the same place on a daily basis, as might be the case for flocks of gulls or individual raptors.

David and Barbara also collected secondary feathers and tail feathers. As there is a difference between the outer tail feathers of adult and first-year birds they were able to show that early moulters included a higher proportion of first-year birds. The paper is well worth a read. David W. Snow & Barbara Snow (1976) Post-breeding Moult of the Lapwing, Bird Study, 23:2, 117-120

As far as I can ascertain, nobody has tried to use this technique again. I feel partially responsible, having written a follow-up paper with Clive Minton that pointed out some flaws in the methodology. These related to a lack of linearity in the progression of primary moult, as measured using the normal score of 0 to 50 based on 0-5 for the ten individual feathers, and the time taken to complete moult once the last primary has been dropped. Using data from Lapwing caught in cannon-net catches in the English Midlands, Clive Minton and I found that Lapwing moult starts very early, with median commencement and completion dates of about 7 June and 29 September – an estimated duration of 114 days and much longer than that suggested in the figure produced by the Snows. G. F. Appleton & C. D. T. Minton (1978) The primary moult of the Lapwing, Bird Study, 25:4, 253-256.

Lapwings are strange

Moulting Curlew

An August high-tide roost. Perhaps Curlew feathers could be collected at low tide?

Most waders that we see in the UK have distinct moult and migration phases to the post-breeding portion of their annual cycle.  After having successfully raised a brood of youngsters or attempted so to do, Turnstones, Bar-tailed Godwits, Knot etc. leave their nesting areas in the high Arctic and fly thousands of kilometres, arriving on our shores in July and August. Although some populations, such as most Dunlin of the schinzii race, only pause to fatten up and then move on to moult further south in northern Africa, many waders that use the UK during autumn undergo a full moult. One can imagine circumstances in which a small flock of inland-moulting Curlew that use the same roost site on a daily basis might be studied in the same way as the Snows studied their Buckinghamshire Lapwings, as long as the lengths and patterns on individual feathers allow the primary number of some of the individual primaries to be assigned with a degree of certainty.


Lapwings were the first birds to be ringed in Britain & Ireland (in 1909). They appear in the logo of the BTO Ringing Scheme

Unlike most of their wader cousins, many Lapwings migrate while moulting their primary feathers. Arctic species have to make long-hop migrations and are restricted in their choice of feeding areas by the distribution of estuaries but Lapwings make short movements and can break their journeys as often as they like. The North Sea is the biggest barrier they face when making journeys from far east in Russia but a crossing from the Netherlands to Norfolk is less than 150 km. Lapwings arriving on the east coast of England have been seen to have gaps in their primaries, despite the fact that these feathers deliver most of the lift and propulsion.

Moult strategy is not the only strange thing about Lapwings; they have also been shown to exhibit abmigration, as described by Chris Mead in a paper with Jim Flegg and Chris Cox in 1968. Although most British-bred Lapwings return to their natal areas to breed, as shown by Pat Thompson et al in 1994, a small number of birds breed a long way from where they were hatched, including Russia, Norway and Sweden. The birds that go on to breed in continental Europe are assumed to join flocks which happen to be travelling east in spring. Given that British-hatched birds as old as 12 years of age have been found breeding in Russia, it is assumed that, having once travelled to a new breeding area, Lapwings will repeat the journey each year. Genetic mixing at large geographic scales would potentially explain a lack of morphological variation across the large range of the species.

Collect some feathers

Moult is currently only studied when birds have been caught but perhaps it might be possible to use digital photography to establish the primary moult duration of colour-ringed individuals or to use the Snows’ technique of collecting feathers from a moulting flock of birds over a period of a few weeks.  On an annual basis there may even be opportunities to monitor change?  A reduced rate of moult, as measured through the collection of discarded primaries, could provide a way to assess inter-annual variation in stress. I wonder if moult periods have increased for birds on the East-Asia Australia Flyway, where they are experiencing reductions in feeding opportunities on their southward migration via the Yellow Sea? Wouldn’t it be interesting if a technique first described by the Snows forty years ago could be used by a new generation of wader biologists when investigating the latest issues of conservation concern?

GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.



Oystercatchers: from shingle beach to roof-top

After over 150 years of successful exploitation of new breeding areas, there are signs that UK Oystercatchers are experiencing predation problems in the Scottish hills and facing disease-related issues on at least one Welsh estuary.

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Oystercatcher parents can fly off in search of food for chicks (Tómas Gunnarsson)

There are Oystercatchers flying over our Norfolk garden with worms to take back to their chicks, travelling up to a mile each way on feeding trips. This commuting behaviour opens up nesting opportunities not available to more conventional wader chicks which find food for themselves, albeit with some coaching. A pair of Oystercatchers can nest on the island of a former gravel pit and move up and down a river valley, to feed in wet grassland, pastures and arable fields, or hatch their chicks on the flat roof of a school and probe for worms on the playing fields. This flexibility has facilitated the spread of the species in England, and may be helping to compensate for declining numbers in the core breeding areas of Scotland.

A 150-year story of expansion

P1000520The Oystercatcher is a very distinctive and noisy bird. When pairs move into new areas they get noticed, providing us with a reliable history of their range expansion over the last two centuries. We might not now be surprised to see breeding pairs well inland, in lowland river valleys or on upland sheep pasture, but these were solely coastal breeders until about 1840, when the first pairs were recorded inland of the north Grampian coast. This nesting behaviour spread within Scotland and reached the English side of the Solway in about 1900 and Northumberland twenty years later.  You can read more in The Historical Atlas of Breeding Birds

The left-hand map below, from Bird Atlas 2007-11, illustrates the continuation of the expansion of the Oystercatcher breeding range between 1968-72, when the first few pairs had established themselves on gravel pits in the English Midlands, through to 2008-11, when pairs were well spread through English counties north of the M4. Oystercatchers have continued to colonise new counties; areas occupied over the last forty years are shown as red triangles, with larger ones being more recent.


Maps of Oystercatcher breeding distribution from Bird Atlas 2007-11, which was a joint project between the Briitish Trust for Ornithology, BirdWatch Ireland and the Scottish Ornithologists’ Club

At first glance, all looks well. However, the right-hand map, which shows the change in abundance between the breeding season surveys of 1988-91 and 2008-11, tells a different story. Densities have been increasing in England (pink colours – darker means higher increase) but there have been major declines across much of Scotland (grey colours – darker means bigger drop).

websAlthough there has not been a large drop in the number of wintering Oystercatchers across the whole of the United Kingdom, the declining number of breeding birds in Scotland may well be to blame for the drop in winter Wetland Bird Survey (WeBS) counts for the country.  The graph alongside suggests that Scottish estuary counts are down by nearly 50% since the peak counts of 2002/03.

Breeding Season


Schematic summary of migration of Oystercatchers ringed or recovered in Britain & Ireland, from Time to Fly by Jim Flegg (BTO)

Oystercatchers nest early in Britain and Ireland and most will have been on territory for several weeks by the end of March. At the same time, there can still be big flocks on the coasts. Some of these are young birds, which won’t breed until two or three years of age, but others will be adults that are fattening up in preparation for migrations to countries such as Iceland and Norway.  Oystercatchers breed beyond the Arctic Circle and all the way to the northern tip of both countries, where spring arrives several weeks later than it does in the UK.

Vero Oyc.jpg

Verónica Méndez-Aragon

When choosing a territory, a pair of Oystercatchers will look for food and somewhere to place a nest. The archetypal nest site might be on a beach, where the eggs blend in with the shingle that forms the nest cup, marine invertebrates can be collected from below the high tide-line and earthworms may be available on near-by fields, golf-courses or lawns, but the species has learnt to breed in a wide range of habitats.  When selecting somewhere to lay a clutch, usually of 2 to 3 eggs, a simple stretch of the imagination can turn the image of a beach into a river-bank, a gravel track or a bare patch in a field.

Ben Darvill

Three Oystercatcher chicks on the roof of The Cotterell Building at the University of Stirling (Ben Darvill / BTO Scotland)

Adding in a third dimension takes Oystercatchers to the flat roofs of buildings, such as those of Stirling University.  Here, all that lies between the fox-free shingle roof and worm-rich lawns below is a vertical drop for the chicks, when they are old enough. High-rise living is an international trait in Oystercatchers; one of the birds ringed in Norfolk by the Wash Wader Ringing Group nested in a window-box in Norway and the practice of roof-nesting is common in the Netherlands.

Oystercatchers look after their chicks for much longer than other wader parents.  Most wader chicks start finding their own insect food from day one, following their parents as they learn to pluck prey from the undersides of plant leaves or from the surface of mud and grass mosaics. Oystercatcher chicks expect a lot of their food to be brought to them. Roof-nesting chicks have no choice other than to wait for dinner to be delivered whilst those on the ground are able to do some of the work themselves.  Youngsters will beg for food for several weeks, even when they can fly, extending the parenting period beyond that which is normal for most waders. The team studying the changing migratory behavior of Icelandic Oystercatcher has found youngsters on mussel beds begging for food in October. (See Migratory Decisions for Icelandic Oystercatchers)

Population Trends

The Oystercatcher is an amber-listed species of conservation concern in the UK, to reflect the importance of these shores to the European breeding population of the species and their reliance outside the breeding season on a small number of estuaries. Although we know that individuals can live for up to 40 years, all is not completely rosy for the species, with predation and food supplies causing problems.

SAMPLED_5990014_300____As has been discussed in the recent Moorland Forum, ‘Understanding Predation report, declines in Oystercatcher numbers have occurred in some moorland parts of the range and there has been a drop in numbers of 29% across Scotland as a whole, since the start of the Breeding Bird Survey in 1995.  The English population had increased by 56% in the same period but this does not compensate for the numerically larger losses from the core northern areas. Local representatives and researchers who contributed to the Moorland Forum report highlighted crows, foxes, buzzards and ravens as the four main predators that threaten the success of breeding Oystercatchers.

Coastal food supplies are critical for Oystercatchers in the winter months and for at least the first two summers of a young bird’s life.  While they take a wide range of shellfish and worms, one of the key elements of the diet on many estuaries is cockles. In the past this has brought Oystercatchers into conflict with cockle fisheries. There was a major controversy in the 1970s when, at the behest of cockle fishers and despite the objection of conservationists in the UK and in Norway, permission was given to shoot 10,000 Oystercatchers on the Burry Inlet in South Wales – and embarrassment when cockle numbers continued to decline.


These cockles have died very recently (image from CEFAS report)

The latest cockle problem is affecting both birds and people, again on the Burry Inlet but also in sites as far apart as the Dee, the Wash and the Dutch coast. Mass die-offs of young cockles are happening in most years, caused by three new parasites, first identified in Spain, America and Portugal, the worst of which causes the haplosporidian infection. In the five winters up until 1999/2000, the average peak count for Oystercatcher on the WeBS count on the Burry Inlet was 17,188, dropping in each of the next three periods to reach 12,195 in the five years up until 2014/15. This represents a 30% decline.

With no available treatments and with the parasites spreading into new areas, life could get tough for human cockle-gatherers and flocks of Oystercatchers, which rely on shellfish for their income and survival, respectively. You can read more about these issues in a CEFAS report which focuses on the Burry Inlet.

Summary: caring, spreading, declining and threatened by disease

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Unlike most wader parents, Oystercatchers find food to feed to their chicks (Tómas Gunnarsson)

  • Cockle die-offs have not as yet had a major, national population-level effect on wintering Oystercatchers but the presence of this threat to Oystercatchers and to other species that feed on young cockles, such as Knot and Turnstone, emphasises the need for continued monitoring and the value of WeBS counts.
  • Breeding Oystercatchers are in decline in the uplands and there is agreement that the role of predators in the moorland environment needs to be better understood. The Moorland Forum report mentioned above also focuses on four red-listed species: the near-threatened Curlew (see separate WaderTales blog), Lapwing, Grey Partridge and Black Grouse.
  • The Oystercatcher has been successfully expanding its breeding range and making use of new nesting opportunities for at least 150 years. Increases in England are, to some extent, compensating for declines in Scotland.
  • The fact that parents collect food for their young opens up breeding opportunities in areas where there are inadequate supplies of food adjacent to safe nesting sites. Clever birds!

This is a modified version of an article that first appeared in Shooting Times & Country magazine.

GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.



Are there costs to wearing a geolocator?

If you’re thinking of using geolocators to study bird migration then here’s a paper that you should read.


Whimbrels on the move (Tómas Gunnarsson)

Devices attached to waders (shorebirds) are adding hugely to our understanding of their movements, and informing plans for the conservation of threatened species, but how safe are these devices for the individual birds that carry them? Emily Weiser and 49 coauthors have reviewed the available evidence in a recent paper Effects of geolocators on hatching success, return rates, breeding movements, and change in body mass in 16 species of Arctic-breeding shorebirds, published in Movement Ecology.

spoi camilo carneiro

Whimbrel wearing a geolocator (Camilo Carneiro)

Marking birds is not without cost. Catching a bird to fit a ring, however light and however expertly applied, subjects the individual to extra risk. Perhaps the ring might get wool tangled around it for instance? Logic suggests that every extra device, from colour-rings through to a harness that carries a satellite tag, adds mass and potential problems. This paper focuses on geolocators – the half-way house between satellite tags and colour-rings, in terms of weight. I find it encouraging that so many scientists have combined in this review of the way that geolocators affect birds’ lives. By providing their data for analysis, they remind us that professional ornithologists have a shared concern for the birds that they work on. As people, they want to minimise the effects on individual birds and, as scientists, they need to reassure themselves that tagged individuals are providing data that are representative of other birds of the same species.

What are geolocators?

Emily Weisser Semi

This Semipalmated Sandpiper carried a geolocator for two years (Emily Weiser)

Geolocators collect information on place and time. Unlike satellite tags, which can relay information from the bird to the scientist on a day-to-day basis, geolocators have to be deployed and then retrieved, so that data can be down-loaded. In the intervening period, these tiny devices record the time of dawn and dusk, information that can be decoded to reveal daily locations, apart from during the periods of spring and autumn equinoxes and if there is heavy cloud.  Geolocators are particularly useful for waders, as most of them live in very open environments (but less good for nocturnal species such as woodcock).

The data used in this paper relate to geolocators weighing between 0.8g and 2.0g, representing 0.1– 3.9 % of mean body mass of the species to which they were applied. They were attached to 16 species of migratory shorebirds, including five species with between 2 and 4 subspecies, making a total of 23 study taxa. The smallest species was only 26 grammes and the largest was just over a kilogramme. Birds were tagged at 23 breeding and eight nonbreeding sites, spread throughout the world.

Geolocators can be attached to harnesses and sit on the back of birds or, as in most cases studied here, attached to a ring or flag on a bird’s leg. The paper looks at the different effects of tags mounted in different ways.

Invaluable Data

Red-n-phal GFAMany wader populations are in trouble. Of the eight curlew species, for instance, one or two species are probably extinct, three others are endangered, vulnerable and near-threatened and only three are not causing concern

Establishing migratory routes and the timing of movements is a critical part of understanding the migration strategies of waders. The results collected from geolocators have important consequences for conservation and are truly fascinating. Who would have believed that Red-necked Phalaropes breeding in Shetland (north of Scotland and west of Norway) would migrate west and south to spend the winter on the surface of the Pacific Ocean between Galapagos and Ecuador? Geolocator tagging reveals Pacific migration of Red-necked Phalarope Phalaropus lobatus breeding in Scotland. Smith, M., Bolton, M., Okill, D.J., Summers, R.W., Ellis, P., Liechti, F. & Wilson, J.D. Ibis. DOI: 10.1111/ibi.12196

Waders operate at a truly global scale, with Bar-tailed Godwits making phenomenal journeys directly from Alaska to New Zealand. This species and others using the East Asian-Australasian flyway are causing major concerns for wader biologists, who have measured huge losses in populations wintering in Australia, New Zealand and south-east Asia. Ringing and colour-ringing had shown that birds fly north each spring to eastern Siberia and Alaska via the coast of eastern Asia – countries such as South Korea and China where there are major development pressures upon estuaries. Simultaneous declines in summer survival of three shorebird species signals a flyway at risk. Theunis Piersma,Tamar Lok, Ying Chen, Chris J Hassell, Hong-Yan Yang, Adrian Boyle, Matt Slaymaker, Ying-Chi Chan, David S Melville, Zheng-Wang Zhang, Zhijun Ma. Journal of Applied Ecology. DOI: 10.1111/1365-2664.12582

MUv116n2coverIdentifying key staging sites, such as the northern end of the Sakhalin peninsular, was possible thanks to the deployment of geolocators, as shown in this paper. Movement patterns of Sanderling (Calidris alba) in the East Asian–Australasian Flyway and a comparison of methods for identification of crucial areas for conservationSimeon Lisovski, Ken Gosbell, Maureen Christie, Bethany J. Hoye, Marcel Klaassen, Iain D. Stewart, Alice J. Taysom and Clive Minton. Emu. DOI 10.1071/MU15042

Using this information, conservation organisation and governments have started to work together to campaign for more sympathetic development of key areas. Conservation without borders – solutions to declines of migratory shorebirds in the East Asian–Australasian Flyway. Judit K. Szabo, Chi-Yeung Choi, Robert S. Clemens and Birgita Hansen. Emu. DOI 10.1071/MU15133

This is just one of many examples of the use of geolocators to fill gaps in migratory stories for waders. Geolocators are also being used to establish wintering areas for breeding species (e.g. Knot in South America) and to assess remotely whether individuals nest successfully. Using Geolocator data  to reveal incubation periods and breeding biology in Red Knots Calidris canutus rufa. Burger J, Niles L J, Porter R R & A D Dey. Wader Study. 119(1): 26–36.


It is not possible to reproduce all of the results in the paper here, or to list all the caveats presented by the authors, but these are the salient points. Anyone considering using geolocators on waders/shorebirds will want to read the whole paper in detail.

  • Importantly, no negative effects of geolocators were detected for most species of shorebirds – including some that migrate huge distances.
  • For some small-bodied taxa (mean body mass ≤58 g), there were substantial negative effects. Geolocators reduced nest success, hatching rate, and/or return rate for two small-bodied species – Semipalmated Sandpipers and Arcticola Dunlin.
  • Changing the way that a geolocator is mounted on the leg can have consequences in terms of return rates and damage to eggs. Simple changes, such as rounding the corners of flags may reduce problems.
  • Studies of the same species in different areas produced different results, in terms of the impacts of geolocators.
  • The findings suggest that guidelines for the relative mass of devices, as developed for backpack-style attachments, may be too liberal for leg-mounted tags. The graph presented in the paper suggests that negative effects may be detected when the tag and attachment together weigh more than 1.5% of body mass.
  • It is not unusual for a wader to live for more than ten years; the studies that contribute to this paper are mostly of short duration and cannot assess long-term effects of tags.
waders and spume TGG

Tómas Gunnarsson

To learn more please read the paper: The effects of geolocators on hatching success, return rates, breeding movements, and change in body mass in 16 species of Arctic-breeding shorebirdsEmily L. Weiser, Richard B. Lanctot, Stephen C. Brown, José A. Alves, Phil F. Battley, Rebecca Bentzen, Joël Bêty, Mary Anne Bishop, Megan Boldenow, Loïc Bollache, Bruce Casler, Maureen Christie, Jonathan T. Coleman, Jesse R. Conklin, Willow B. English, H. River Gates, Olivier Gilg, Marie-Andrée Giroux, Ken Gosbell, Chris Hassell, Jim Helmericks, Andrew Johnson, Borgný Katrínardóttir, Kari Koivula, Eunbi Kwon, Jean-Francois Lamarre, Johannes Lang, David B. Lank, Nicolas Lecomte, Joe Liebezeit, Vanessa Loverti, Laura McKinnon, Clive Minton, David Mizrahi, Erica Nol, Veli-Matti Pakanen, Johanna Perz, Ron Porter, Jennie Rausch, Jeroen Reneerkens, Nelli Rönkä, Sarah Saalfeld, Nathan Senner, Benoît Sittler, Paul A. Smith, Kristine Sowl, Audrey Taylor, David H. Ward, Stephen Yezerinac and Brett K. Sandercock. Movement Ecology 20164:12. DOI: 10.1186/s40462-016-0077-6


I am sure that members of panels charged with the task of issuing permits to those engaged in migration research will find this study tremendously useful, especially as so much detail has been made freely available within the paper and in supplementary material. It is hugely encouraging that, for most species, there is no evidence that the costs to individuals outweigh the potential conservation benefits. Future decisions to deploy devices on small-bodied shorebirds will be made on a case-by-case basis, weighing the potential impacts on individuals and populations against the value of improved knowledge of migratory movements.

BOU conference 2017

BOU confMost ornithological conferences now include talks that reveal new insights gained using geolocators or other devices carried by migrating birds. The spring 2017 BOU conference From avian tracking to population processes will aim to take this work one step further, by bringing together ornithologists and ecologists, in order to explore how tracking individuals can help to address questions about population processes and their implications for conservation and management.

GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.


Whimbrels on the move

You may hear the distinctive seven-note call of a Whimbrel overhead in late April or May but where is it going and where has it been?

better top pic

Many pairs of Whimbrel nest in the flood-plains of Iceland’s rivers (Tómas Gunnarsson)

In a new paper in Wader Study, Tómas Gunnarsson and Guðmundur Guðmundsson have analysed the ringing recoveries of Icelandic Whimbrel and demonstrated that many probably make non-stop flights from Iceland to western Africa.  The study also helps to explain the timing and origins of flocks of Whimbrel in different parts of the British Isles in spring and late summer.

Migration and non-breeding distribution of Icelandic Whimbrels Numenius phaeopus islandicus as revealed by ringing recoveries: Tómas Grétar Gunnarsson and Guðmundur A. Guðmundsson.  The full paper is available to subscribers to Wader Study but a summary is available here.

Whimbrels in Iceland

It is estimated that 250,000 pairs of Whimbrel  breed in in Iceland, representing 25% of the combined global population for all seven subspecies of Whimbrel and making Iceland a very important country for the species. The Icelandic breeding population is believed to be relatively stable but others, such as those in North America, are in decline.

1 eldgos

There are two blogs about how volcanic dust affects Whimbrel. In the long-term volcanic ash provides important fertilizers but short term effects can be seen in breeding success.

The Whimbrel is one of the commonest of Iceland’s breeding wader species, with most nests estimated to be at elevations lower than 200m and particularly along river flood-plains.

Iceland is a country in a state of constant flux, both because of geothermal activity and the subsequent physical processes associated with wind and water flow, and as a result of human interventions. Volcanic ash has been shown to affect the breeding success of Whimbrels in the short term and their distribution in the longer term. Land use is also changing rapidly, particularly as a result of afforestation and the ways that land is farmed, and work is ongoing to understand how these processes might impact upon breeding waders, including Whimbrels.

Movements of Icelandic Whimbrel

nesting whimbrel

Nesting Whimbrel hunkers down in heathland vegetation – a very different habitat to the mud and mangroves of West Africa (Tómas Gunnarsson)

Over 6000 Whimbrels have been ringed in Iceland since 1921, with 95% of these caught as chicks. 35 Icelandic-ringed Whimbrels have been recovered abroad and 4 foreign-ringed Whimbrels have been found in Iceland.  In their paper, Tómas and Guðmundur show that most of the winter records of Icelandic birds are in west Africa, between Mauritania in the north and Benin and Togo in the south, but that there are two January records in Spain, suggesting that some individuals don’t travel further south than Europe.  Spain and Portugal cannot be particularly important wintering areas for the species, however, as Whimbrel counts across Spain and Portugal don’t exceed 1000 birds, which represents a tiny part of the Icelandic population, even if they are all assumed to originate from there.


Reproduced from Gunnarsson & Gudmundsson 2016 with permission from Wader Study

Spring and autumn Whimbrel records that link Iceland with Britain and Ireland show strikingly different distributions for the two seasons.  There are eight recoveries in the British Isles on spring passage; 1 in Ireland and 7 in western counties of the UK. There is only one autumn passage record (in the Outer Hebrides), despite the fact that autumn shooting of Curlew, which did not stop until 1981, might have been expected to have produced recoveries of similar Whimbrel. This strongly suggests that, while some whimbrel stop off on northwards migration, the southerly journey is straight to Africa. We know that this is possible, because a satellite-tagged Whimbrel was tracked making a direct flight from Iceland to Guinea-Bissau in late summer 2007.

Counts and recoveries of British birds

Some of the big WeBS counts for Whimbrel are made in the late summer, with over 1500 birds reported on the Wash (August), nearly 300 along the North Norfolk coast (August) and nearly 200 in July in each of Chichester Harbour (Hampshire) and Morecambe Bay.  Largest counts in spring are mainly in the west and all in April, with 331 on the Severn, 339 on the Ribble and 654 in the Fylde area but one east coast site (Breydon Water in Norfolk) has had a spring count of 137. Although April & May flocks might seem large, they should be viewed in context – at least 500,000 Whimbrel travel back to Iceland each year.

The only British-ringed Whimbrels to have been found in Iceland have been two satellite-tagged birds, one of which is mentioned above, but metal-ringed birds have returned to breeding grounds in Finland, Russia and Sweden. Given that this new paper suggests no links between eastern Britain and Iceland in the autumn, it is likely that the large number of birds that spend the moult period on east coast estuaries such as the Wash are mainly of continental origin. The same is probably true for late-summer gatherings, such as the ones in Chichester Harbourand Morecambe Bay.


Tómas Gunnarsson

In order to understand more about spring flocks of Whimbrel in the UK, ringing and satellite tagging has been taking place in the Lower Derwent Valley (East Yorkshire). Birds tagged here have flown to both Iceland and Sweden which indicates that Icelandic and continental birds gather together in April and May flocks. Despite this mix of subspecies in Yorkshire, the lack of ringing recoveries of Icelandic birds in the east of the UK suggests that continental birds make up the majority of spring flocks in the east.

To summarise: if you hear a Whimbrel calling overhead in the autumn it is probably of continental origin, especially in the east. On spring passage, a seven-note call in the west may well have an Icelandic twang but in the east it could sound that little bit more Scandinavian. If only we could tell them apart.

What next?


Tómas Gunnarsson

This analysis of metal-ringed birds sets the context for new studies to understand the migration strategies of individual Icelandic birds, using geolocators and satellite tags.

The first paper using these data appeared in Nature’s Scientific Reports. In it, José Alves and his colleagues show that four birds completed the autumn migration in one flight. On return in spring, two of these birds stopped off in Ireland and two flew straight to Iceland. With further research it should soon be possible to understand how these epic sea crossings from Iceland to Africa are affected by prevailing winds and varying weather patterns, whether individuals use the same strategies in different years and if a juvenile can make it all the way to Africa on its maiden flight. Meanwhile, you can help with the studies of migration by looking out for and reporting colour-ringed Whimbrel. Most of the ones seen in Britain & Ireland will have been marked by researchers in Iceland and they will be delighted to hear news of their birds at

 GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.